I'm new to MTG. I have Horizon Chimera which has "Whenever you draw a card, gain 1 life." Does that mean you gain 1 life at the beginning of every round, when you draw a card? (That seems over-powered.)
- Draw Step
504.1. First, the active player draws a card. This turn-based action doesn’t use the stack.
You perform the "draw a card" keyword action at the beginning of your turns, and that's the action on which Horizon Chimera's ability triggers, so it does indeed trigger.
Keep in mind that the ability triggers for every card drawn, even when instructed to draw multiple cards.
120.2. Cards may only be drawn one at a time. If a player is instructed to draw multiple cards, that player performs that many individual card draws.
This differs from "whenever you lose life" (which triggers once every time you lose life, no matter how much life you lose) and "whenever [something] deals damage" (which triggers once every time it deals damage, no matter how much damage it deals).